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Upon performing colorimetric determination of chromium with diphenyl-carbazide (DPC), the following were found. The color development proceeded not only in dilute sulphuric acid solution, but also in solutions of HNO3, HCl, HClO4 and CH3COOH or in mixed solutions of these acids. Wide concentration ranges (about 0.01-0.5N) of these single acids allowed perfect development of the Cr6+ coloration with DPC. Mixed solutions of 0.1-1% of these acids also resulted in perfect color development. HC1O4 proved to be the most excellent oxidant of Cr3+ to Cr6+ for the reaction with DPC compared with Mn02 and Pb02. The mixed acid (HC104+H2SO4) was more suitable than single HC1O4 for this oxidation.

Experimental investigation of actual problems in the colorimetric determination of chromium with diphenylcarbazide.